1. Field of the Invention
The present invention relates to a method for processing a backlight image and a device thereof, and more specifically, to a method for compensating a darker region of a backlight image and a device thereof.
2. Description of the Prior Art
With the development of technology, analog tools are gradually replaced by digital products. Digital camera is the most representative example. Compared with a traditional camera, images are digitalized into digital signals by the digital camera. Then the digital signals are saved into a file form in a memory device. A user can connect the digital camera to a computer system, meaning that the images can be saved in a hard disk. In such a manner, the images took by the digital camera can be displayed on a display device, or output by a printer immediately. Moreover, the user can also edit the saved images using an image editing tool to create images with special effects.
It is unavoidable for users to take photos of backlight image. Backlight image means an image having a dark object with a bright background. For improving this drawback, many methods for compensating a backlight image have been developed. The prior arts involve overcompensating the whole background based on the entire image, or compensating the backlight image in two stages through fuzzy technology. The methods mentioned above usually result injunction effect of the image. For example, please refer to FIG. 1. FIG. 1 is a γ correction curve of two-stage backlight image compensating method according to a prior art. The γ correction curve presents a corresponding relationship of brightness before and after being adjusted. The region that the unadjusted luminance value smaller than ‘A’ is the darker part of the backlight image. The two-stage compensating method according to the prior art involves only processing the darker part of the backlight image in a brightness-enhancement way. Therefore, there is a considerable discontinuity of color level at the border between two image-compensating stages (at the unadjusted luminance ‘A’). That affects smoothness of the color level and then lowers the quality of the image. For solving this problem, another backlight image compensating method has been disclosed in the paper, “Detection and Compensation Algorithm for Backlight Images with Fuzzy Logic and Adaptive Compensation Curve”, issued by C. L. Chin and C. T. Lin on International Journal of Pattern Recognition and Artificial Intelligence. However, the amount of calculations in the method is huge because of the extra compensation region detection. That will reduce the image processing efficiency. Therefore, how to develop a method to balance the image quality and calculation efficiency is the main subject of the present image processing technology.